1. Field of the Invention
The invention relates to an eraser, composed of fillers, a binder of a thermoplastic material based on synthetic rubber as the binder, and possibly other additions.
2. Description of the Prior Art
In a known eraser of this type, described in Belgian Pat. No. 673,229, materials, such as, polychloroprene, chlorosulfonated polyethylene, polybutadiene, polyacrylonitrile or polyisobutylene are used as binders. Moreover, factice can also be used in this case.
However, this eraser is disadvantageous primarily because of either an additional vulcanization process or a peroxidic crosslinking is required for the particular binders. In addition, as a rule, large amounts of softeners, such as, for example, chloroparaffins, which have a great tendency to migrate, are required. When factice (chlorosulfur rape oil) is used which is a natural product whose composition cannot be exactly defined, it is not possible to obtain consistency in the final products without continuous adjustments to the process, particularly, with respect to the hardness, abrasion properties, or the absorption of softeners.
In accordance with another proposal in U.S. Pat. No. 3,738,951, a butadiene-styrene block polymer with a butadiene to styrene ratio of 4:1 to 1:1 (80:20 to 50:50 percent by weight) is to be used as the binder. Furthermore, in this case, the use of factice and of a naphthenic oil as the softeners is suggested.
Also, there are the disadvantages resulting from the problems created by the use of factice, and the aromatic substances in the naphthenic oils may be physiologically harmful.